libsyntax: Accept `use foo as bar;` in lieu of `use bar as foo;`

The old syntax will be removed after a snapshot.

RFC #47.

Issue #16461.

3 files changed, 16 insertions, 8 deletions

diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs
index 7d9a23e91ba..d93b2800879 100644
--- a/src/libsyntax/ast.rs
+++ b/src/libsyntax/ast.rs
@@ -1114,11 +1114,11 @@ pub type ViewPath = Spanned<ViewPath_>;
 #[deriving(Clone, PartialEq, Eq, Encodable, Decodable, Hash, Show)]
 pub enum ViewPath_ {
 
-    /// `quux = foo::bar::baz`
+    /// `foo::bar::baz as quux`
     ///
     /// or just
     ///
-    /// `foo::bar::baz ` (with 'baz =' implicitly on the left)
+    /// `foo::bar::baz` (with `as baz` implicitly on the right)
     ViewPathSimple(Ident, Path, NodeId),
 
     /// `foo::bar::*`
diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index f6db577a004..50db5029904 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -5309,6 +5309,7 @@ impl<'a> Parser<'a> {
         match self.token {
           token::EQ => {
             // x = foo::bar
+            // NOTE(stage0, #16461, pcwalton): Deprecate after snapshot.
             self.bump();
             let path_lo = self.span.lo;
             path = vec!(self.parse_ident());
@@ -5391,7 +5392,7 @@ impl<'a> Parser<'a> {
           }
           _ => ()
         }
-        let last = *path.get(path.len() - 1u);
+        let mut rename_to = *path.get(path.len() - 1u);
         let path = ast::Path {
             span: mk_sp(lo, self.span.hi),
             global: false,
@@ -5403,9 +5404,12 @@ impl<'a> Parser<'a> {
                 }
             }).collect()
         };
+        if self.eat_keyword(keywords::As) {
+            rename_to = self.parse_ident()
+        }
         return box(GC) spanned(lo,
                         self.last_span.hi,
-                        ViewPathSimple(last, path, ast::DUMMY_NODE_ID));
+                        ViewPathSimple(rename_to, path, ast::DUMMY_NODE_ID));
     }
 
     /// Parses a sequence of items. Stops when it finds program
diff --git a/src/libsyntax/print/pprust.rs b/src/libsyntax/print/pprust.rs
index 4ee73406f03..be4043bd73b 100644
--- a/src/libsyntax/print/pprust.rs
+++ b/src/libsyntax/print/pprust.rs
@@ -2262,13 +2262,17 @@ impl<'a> State<'a> {
     pub fn print_view_path(&mut self, vp: &ast::ViewPath) -> IoResult<()> {
         match vp.node {
             ast::ViewPathSimple(ident, ref path, _) => {
+                try!(self.print_path(path, false));
+
                 // FIXME(#6993) can't compare identifiers directly here
-                if path.segments.last().unwrap().identifier.name != ident.name {
-                    try!(self.print_ident(ident));
+                if path.segments.last().unwrap().identifier.name !=
+                        ident.name {
                     try!(space(&mut self.s));
-                    try!(self.word_space("="));
+                    try!(self.word_space("as"));
+                    try!(self.print_ident(ident));
                 }
-                self.print_path(path, false)
+
+                Ok(())
             }
 
             ast::ViewPathGlob(ref path, _) => {